You can use vintage frames and paint them in a color that works with your decor, or you can pick up new frames for very little money. If you plan on changing the artwork regularly you can leave out the glass and simply use the frame.
You can hang children's art from clips that can help you rotate the artwork as your child makes it. You can affix boards to your wall as seen in this picture, you can affix a metal strip and use magnets to hold your children's art or even a drapery rod to hang the artwork from.
Turn children's artwork into a book. You can either make one yourself with scrapbooking supplies and creativity or send the pictures virtually to a professional that will work with you to make a book.
I think it is always a good thing to encourage children to draw and be creative whenever possible and when we are able to display their artwork it gives them a sense of pride, and accomplishment - what's better than that?